What is CVE-2025-66284?

CVE-2025-66284 is a medium-severity vulnerability in Groupsession, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2025-12-12.

How severe is CVE-2025-66284?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Groupsession

CVE-2025-66284

Stored cross-site scripting vulnerabilities exist in GroupSession Free edition prior to ver5.7.1, GroupSession byCloud prior to ver5.7.1, and GroupSession ZION prior to ver5.7.1. A logged-in user can prepare a malicious page or URL, and an…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.001 (3.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

Affected products

Groupsession
Japan Total System Co.,ltd. Groupsession Bycloud — versions prior to ver5.7.1
Japan Total System Co.,ltd. Groupsession Free Edition — versions prior to ver5.7.1
Japan Total System Co.,ltd. Groupsession Zion — versions prior to ver5.7.1

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

vultures@jpcert.or.jp (Vendor Advisory)
vultures@jpcert.or.jp (Third Party Advisory)

Frequently asked questions

What is CVE-2025-66284?: CVE-2025-66284 is a medium-severity vulnerability in Groupsession, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2025-12-12.
How severe is CVE-2025-66284?: Medium severity. CVSS v3 base score is 5.4 out of 10.